Dry bitumen liquid is obtained from oil sands and is further processed in a fluidized bed coker to produce low-boiling petroleum products. The efficacy of this coking process depends upon effective and rapid heat transfer from the fluidized bed solids of the coker to the bitumen feed. This can be enhanced by introducing the bitumen into the coker in the form of fine liquid droplets, thereby significantly increasing the surface area of the bitumen. The greater the surface area, the more effective and rapid the heat transfer to the bitumen. In addition, better heat transfer is achieved if the cross-sectional coverage area of the droplets is increased. The formation of a wide spray of evenly distributed fine bitumen droplets will increase the desired liquid distillate products and decrease the undesired by-products, namely, gas make and coke make.
The bitumen feed is conventionally mixed with steam to produce a two phase mixture and this mixture is injected into the fluid coker through nozzles. The nozzles induce some atomization of the bitumen so that a spray or jet of bitumen droplets is injected into the coker. However, it is our belief that the commercial nozzles available only atomize a portion of the bitumen. We have tested the prior art nozzles used in the present assignees' fluid coker using water and steam as the feed--the indication is that 70-90% of the liquid passed through the nozzle is in a non-atomized form. In addition, the average mean diameter of the atomized liquid droplets produced in the test were in the order of 400 .mu.m for an air to liquid ratio (ALR) value of 0.008; this is larger than desirable for optimal coking of the bitumen to occur.
One aim of the present invention is to provide an improved nozzle that atomizes most of the liquid processed into evenly distributed fine droplets, resulting in desirable droplet surface area of the bitumen when it is subjected to the coking process.
In service, nozzles used to atomize the bitumen feed are subject to high wear rates and a high degree of plugging. Therefore it is desirable to ensure that a nozzle not only atomizes the bitumen effectively but is also erosion resistant in order to minimize replacement and repair costs. This can be achieved by designing a nozzle assembly with a minimum of internal parts. In addition, the nozzle assembly should be "roddable" so that it may be unplugged with a rod.
It is also desirable that a nozzle design be effective over a broad range of gas/liquid ratios because the bitumen feed rate is variable.
It is further desirable that the pressure drop required for achieving satisfactory atomization is not excessive.
The literature teaches that several flow mechanisms can have an effect on reducing liquid droplet size in two phase flow. More particularly it is known:
That longitudinal vibration of stretched liquid droplets (referred to as "ligaments") can cause reduced diameter at the nodal points and corresponding "necking", which can lead to droplet break-up and formation of finer droplets (this is referred to as the "Rayleigh instability"); PA1 That longitudinal stretching or straining of a liquid droplet by an accelerating carrier fluid flow can lead to droplet break-up. Otherwise stated, situating droplets of one fluid in another fluid undergoing acceleration can cause the droplets to undergo shear. When the shear forces overcome surface tension forces, the droplets will deform and can break up (this is referred to as the "elongation effect"); PA1 That mean and fluctuating shear stresses applied to larger droplets can cause the droplets to rotate, then stretch and ultimately divide into smaller droplets. Mean shear effects and stresses can be induced in droplets by turbulent flow and fluctuations of the carrier phase (the "Reynolds stress effect"); PA1 That droplets can collide with each other or an impact surface and break up if generated internal stress exceeds surface tension effects; and PA1 That droplets passing through a supersonic shock wave can break up due to the effect of the sudden pressure rise. PA1 the first contraction section should accelerate the mixture to supersonic velocity--the possibility is then created for generating a flow of relatively small droplets such as in "bubbly" flow due to the elongation of the flow and secondly generating a shock wave in the diffuser due to the lower speed of sound value. If a shock wave is created, it will assist in droplet size reduction; PA1 as previously stated, the second contraction section should accelerate the mixture more than that achieved by the first section. We successfully used a section that provided about twice the acceleration. If the fine droplets produced by the first contraction and diffuser sections are to be further reduced in size, it is necessary to subject them to relatively increased elongation and shear stress; and PA1 the diffuser section should increase the diameter of the flow passageway sufficiently so that the desired acceleration in the second contraction section can be achieved. However the length of the section needs to be limited to avoid excessive recombination of droplets. We found a 3.degree. section to be satisfactory while a 6.degree. section, total angle, was much less useful. PA1 a straight pipe closed at one end by a valve and connected at the other end with the nozzle; PA1 a pre-conditioning nozzle of reducing diameter positioned coaxially in the pipe bore between its ends; PA1 an inlet upstream of the nozzle, for introducing the steam; and PA1 an inlet, close to and downstream of the nozzle, for introducing the bitumen. PA1 use of the nozzles and active mixing means in connection with a commercial fluid coker demonstrated improved upgraded oil yield; PA1 the nozzle has been shown to be capable of reducing the majority of water droplets in a water/air mixture from about 12,000 .mu.m in the feed to about 300 .mu.m in the jet product and the fine droplets are evenly distributed in the product jet; and PA1 the nozzle is free of working parts and is roddable.
It is the objective of the invention to provide a nozzle assembly, free of moving parts, which can be "rodded" to unplug it and which is designed to incorporate some or all of the previously mentioned flow mechanisms, to combine in efficiently breaking up large liquid droplets in a two phase flow.
It is to be understood that, while the nozzle was developed for service with fluid cokers in the petroleum refining field, it is anticipated that it will find application in other fields where atomizing nozzles are used.